The present invention relates to a dust collecting filter housed within a rotating disk storage device such as a magnetic disk drive or an optical disk drive. More particularly, the present invention is concerned with a rotating disk storage device having an electrostatic filter. The electrostatic filter electrostatically sucks dust suspended in an air flow created with rotation of a disk medium, then separates the dust from air, and collects the dust.
In a magnetic disk drive as one of rotating disk storage devices, the recording density rises with an increase in storage capacity and reduction of size. As a result, the spacing between a recording surface and a head is becoming more and more narrow. At the same time, it has become more important to cope with the problem that very fine dust particles adhere to a surface of a magnetic disk and cause head crash. Assembly of the magnetic disk drive is carried out in a clean room held in a clean air environment, but it is difficult to completely prevent dust from staying in the interior of a disk enclosure. Moreover, an accidental contact of the magnetic disk, which is rotating at high speed, with a head slider may cause the generation of new dust.
The disk enclosure permits ingress and egress of a slight amount of air between the interior and the exterior through a breathing filter. The ingress and egress take pressure balance upon occurrence of a pressure difference between the interior and the exterior of the magnetic disk device. However, fine dust particles penetrating the breathing filter may attract each other and grow larger. Therefore, in a conventional magnetic disk drive, a mechanical filter is mainly used for collecting dust present in the interior of the disk enclosure. Further, an electrostatic filter has also been used. FIG. 1 is a plan view of a conventional magnetic disk drive 1 having a mechanical filter. As a magnetic disk 3 rotates in the direction of arrow A, an air flow flowing in the same direction as the rotating direction of the disk is created on a surface of the magnetic disk. A portion of the air flow enters a corner chamber 8 formed at a corner of a disk enclosure. In the corner chamber 8, a mechanical filter 7 is disposed between an island-like wall portion 6 and a side wall of the disk enclosure.
The mechanical filter 7 is formed such that an activated charcoal filter is surrounded with a charging filter. In addition, the charging filter is surrounded with cloth superior in gas permeability such as gauze. While the air flow, which has entered the corner chamber 8, passes through the mechanical filter 7 and moves again toward the magnetic disk 3, the filter 7 collects dust suspended in the air flow. In the mechanical filter, smaller meshes collect dust suspended in the air flow. Therefore, as the filter is used, dust gradually clogs meshes from the surface to the interior of the filter, with consequent increase of pressure loss and decrease of the dust collection efficiency.
In the mechanical filter, the probability of crash of dust particles against the filter becomes higher as the weight per unit area of the filter formed in a fabric shape increases. An appropriate weight per unit area of the filter is selected according to the size of dust particles to be collected. As the weight per unit area of the filter increases, it becomes possible to collect finer dust particles, but the pressure loss increases and the amount of air passing through the filter becomes smaller. Within the disk enclosure, the air flow is produced by the magnetic disk 3, which rotates at a predetermined number of revolutions. Thus, the number of revolutions and radius of the magnetic disk 3, as well as the number of disks stacked determine the flow velocity of the air flow. If the precision of the mechanical filter is enhanced to collect finer dust particles, the weight per unit area of the filter increases and a deficiency in the air flow velocity can occur. Moreover, even if the pressure loss of the filter increases with use of the filter, it is impossible to increase the air flow velocity. The only measure against a decrease of efficiency is the replacement of filter medium. Thus, in the mechanical filter, it is impossible to attain a satisfactory performance.
A method using 90% clean-up time is known as a method for evaluating the performance of a filter used in a magnetic disk drive. The 90% clean-up time means the time required until dust staying in the interior of the disk enclosure is collected on the filter with rotation of the magnetic disk and the amount thereof decreases 90% relative to an initial value. When the magnetic disk drive using the mechanical filter was measured for 90% clean-up time, it turned out that the 90% clean-up time became longer as the product of the number of revolutions and the diameter of the magnetic disk became smaller. Under the condition that the number of revolutions and the diameter of the magnetic disk were fixed, the 90% clean-up time showed an increasing tendency as the number of stacked disks became smaller. From these facts it can be presumed that the number of revolutions and the diameter of the magnetic disk, as well as the number of stacked disks, have a bearing on the total amount of air flowing through the mechanical filter. In the case of a small-sized magnetic disk drive having a small number of magnetic disks stacked and having a small diameter, a satisfactory dust removal may be impossible.
Japanese Patent Laid-open No. 2000-222854 discloses a technique of affixing an electrostatic charge member (sub-liner) such as electret to a liner for keeping clean the surface of a recording medium in a floppy disk drive (floppy is a registered trademark) (see FIG. 2 in the same document). As the electrostatic charge member, fibers are formed into a non-woven cloth shape as an electrostatic charge attraction member that is then constituted in the form of liner to enhance the dust attraction effect.
Japanese Patent Laid-open No. Hei 3-54790 discloses a technique related to an air cleaner for a magnetic disk drive utilizing an electric charging action. Air passing through the air cleaner is provided with a charging section and a dust attracting section. The charging section is disposed on a charging side for electrically charging dust suspended in air into a positive charge or a negative charge. The dust attracting section is disposed on a downstream side of a flow path to attract the dust having been charged to a positive or negative charge. Japanese Patent Laid-open No. Hei 6-60608 discloses a technique wherein a filter having an electric charging property is used in a positioning mechanism of a magnetic disk drive to enhance the dust collection efficiency.